Wound Healing Apparatus For Promoting Granulation And Epithelialisation At A Tissue Site

ABSTRACT

An apparatus for promoting granulation and epithelialisation at a tissue site having a substantially gas impermeable, flexible mat. A plurality of projections extend from a surface of the substantially gas impermeable, flexible mat, and each projection has a first end connected to the surface and a second end opposing the first end. A flexible membrane is positioned adjacent the second end of at least a portion of the plurality of projections and the flexible membrane is sufficiently flexible to allow deformation of the flexible membrane by the at least the portion of the plurality of projections when a biasing force exerted on the substantially gas impermeable, flexible mat or the plurality of projections is greater than or equal to a threshold force.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/311,873, filed Dec. 6, 2011 which claims the benefit of U.S.Provisional Application No. 61/420,678, filed Dec. 7, 2010, which ishereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to reduced pressure treatmentsystems and more particularly to a wound healing apparatus for promotinggranulation and epithelialisation at a tissue site.

2. Description of Related Art

Clinical studies and practice have shown that providing a reducedpressure in proximity to a tissue site augments and accelerates thegrowth of new tissue at the tissue site. The applications of thisphenomenon are numerous, but one particular application of reducedpressure involves treating wounds. This treatment (frequently referredto in the medical community as “negative pressure wound therapy,”“reduced pressure therapy,” or “vacuum therapy”) provides a number ofbenefits, including migration of epithelial and subcutaneous tissues,improved blood flow, and micro-deformation of tissue at the wound site.Together these benefits result in increased development of granulationtissue and faster healing times. Typically, reduced pressure is appliedby a reduced pressure source to tissue through a porous pad or othermanifold device. The porous pad contains cells or pores that are capableof distributing reduced pressure to the tissue and channeling fluidsthat are drawn from the tissue. The porous pad often is incorporatedinto a dressing having other components that facilitate treatment.

SUMMARY

The problems presented by existing reduced pressure systems and woundhealing pads are solved by the systems and methods of the illustrativeembodiments described herein. An apparatus for promoting granulation andepithelialisation at a tissue site includes a substantially gasimpermeable, flexible mat. A plurality of projections extend from asurface of the substantially gas impermeable, flexible mat, and eachprojection has a first end connected to the surface and a second endopposing the first end. A flexible membrane is positioned adjacent thesecond end of at least a portion of the plurality of projections and theflexible membrane is sufficiently flexible to allow deformation of theflexible membrane by the at least a portion of the plurality ofprojections when a biasing force exerted on the substantially gasimpermeable, flexible mat or the plurality of projections is greaterthan or equal to a threshold force.

In another embodiment, an apparatus for promoting granulation andepithelialisation at a tissue site includes a hollow mat having an innerchamber and a plurality of recesses disposed in proximity to a firstsurface of the hollow mat. An extendable projection is positioned withineach recess and configured to extend from the recess when a pressure(p₁) within the inner chamber is greater than a pressure (p₂) in therecess.

In still another embodiment, an apparatus for promoting granulation andepithelialisation at a wound includes a porous pad having a firstcompressibility. A plurality of granulation promoters are embeddedwithin the porous pad and have a second compressibility less than thefirst compressibility of the porous pad. The granulation promoters arepositioned near a surface of the porous pad. A biasing force applied tothe porous pad or granulation promoters that is greater than or equal toa threshold amount causes the granulation promoters to extend from theporous pad or alters the surface of the porous pad to promotegranulation.

In yet still another embodiment, an apparatus for promoting granulationand epithelialisation of a tissue site includes a porous, reticulatedfoam having a tissue-contacting surface that is sufficiently rough topromote granulation. A hydrogel-forming material is disposed in at leasta portion of the porous, reticulated foam such that the introduction ofa liquid into the porous pad causes the hydrogel-forming material tomoisten and expand, thereby altering the tissue-contacting surface to besufficiently smooth to promote epithelialisation.

In another embodiment, a reduced pressure treatment system foradministering reduced pressure treatment to a tissue site includes areduced pressure source and a manifold in fluid communication with thereduced pressure source to provide a reduced pressure to the tissuesite. The manifold has a tissue-contacting surface in contact with thetissue site, and the tissue-contacting surface has a granulationconfiguration and an epithelialisation configuration such that at leastone of the granulation configurations and the epithelialisationconfigurations is activated by an activation stimulus.

In still another embodiment, a reduced pressure treatment system foradministering reduced pressure treatment to a tissue site includes areduced pressure source and an apparatus fluidly coupled to the reducedpressure source and positioned at the tissue site. The apparatusincludes a substantially gas impermeable, flexible mat. A plurality ofprojections extend from a surface of the substantially gas impermeable,flexible mat, and each projection has a first end connected to thesurface and a second end opposing the first end. A flexible membrane ispositioned adjacent the second end of at least a portion of theplurality of projections and the flexible membrane is sufficientlyflexible to allow deformation of the flexible membrane by the at least aportion of the plurality of projections when a biasing force exerted onthe substantially gas impermeable, flexible mat or the plurality ofprojections is greater than or equal to a threshold force. A drapeformed of substantially impermeable material covers the apparatus andthe tissue site to substantially maintain the reduced pressure at thetissue site.

In another embodiment, a reduced pressure treatment system foradministering reduced pressure treatment to a tissue site includes areduced pressure source and an apparatus fluidly coupled to the reducedpressure source and positioned at the tissue site. The apparatusincludes a hollow mat having an inner chamber and a plurality ofrecesses disposed in proximity to a first surface of the hollow mat. Anextendable projection is positioned within each recess and configured toextend from the recess when a pressure (p₁) within the inner chamber isgreater than a pressure (p₂) in the recess. A drape formed ofsubstantially impermeable material covers the apparatus and the tissuesite to substantially maintain the reduced pressure at the tissue site.

In yet still another embodiment, a reduced pressure treatment system foradministering reduced pressure treatment to a tissue site includes areduced pressure source and an apparatus fluidly coupled to the reducedpressure source and positioned at the tissue site. The apparatusincludes a porous pad having a first compressibility. A plurality ofgranulation promoters are embedded within the porous pad and have asecond compressibility less than the first compressibility of the porouspad. The granulation promoters are positioned near a surface of theporous pad. A biasing force applied to the porous pad or granulationpromoters that is greater than or equal to a threshold amount causes thegranulation promoters to extend from the porous pad or alters thesurface of the porous pad to promote granulation. A drape formed ofsubstantially impermeable material covers the apparatus and the tissuesite to substantially maintain the reduced pressure at the tissue site.

In another embodiment, a reduced pressure treatment system foradministering reduced pressure treatment to a tissue site includes areduced pressure source and an apparatus fluidly coupled to the reducedpressure source and positioned at the tissue site. The apparatusincludes a porous, reticulated foam having a tissue-contacting surfacethat is sufficiently rough to promote granulation. A hydrogel-formingmaterial is disposed in at least a portion of the porous, reticulatedfoam such that the introduction of a liquid into the porous pad causesthe hydrogel-forming material to moisten and expand, thereby alteringthe tissue-contacting surface to be sufficiently smooth to promoteepithelialisation. A drape formed of substantially impermeable materialcovers the apparatus and the tissue site to substantially maintain thereduced pressure at the tissue site.

In still another embodiment, a reduced pressure treatment system havinga reduced pressure source and a manifold may be paired with any of theapparatuses described herein.

In another embodiment, a method for selectively promoting granulationand epithelialisation of a tissue site includes positioning a pad havinga tissue-contacting surface at the tissue site. Reduced pressure isapplied to the tissue site when the tissue-contacting surface is in afirst configuration to promote granulation. The first configuration ofthe tissue-contacting surface is changed to a second configuration. Areduced pressure is applied to the tissue site when thetissue-contacting surface is in the second configuration to promoteepithelialisation.

Other objects, features, and advantages of the illustrative embodimentswill become apparent with reference to the drawings and detaileddescription that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view with a portion shown incross-section of a reduced pressure treatment system for administeringreduced pressure treatment to a tissue site according to an illustrativeembodiment;

FIG. 2A illustrates a cross-sectional view of an illustrative,non-limiting embodiment of a wound healing apparatus of the reducedpressure treatment system of FIG. 1 in a state for promotingepithelialisation;

FIG. 2B illustrates a cross-sectional view of the wound healingapparatus of FIG. 2A in a state for promoting granulation;

FIG. 3 illustrates a cross-sectional view of another illustrative,non-limiting embodiment of a wound healing apparatus;

FIG. 4A illustrates a cross-sectional view of another illustrative,non-limiting embodiment of a wound healing apparatus in a state forpromoting epithelialisation;

FIG. 4B illustrates a cross-sectional view of the wound healingapparatus of FIG. 4A in a state for promoting granulation;

FIG. 4C illustrates a cross-sectional view of another illustrative,non-limiting embodiment of the wound healing apparatus of FIG. 4A;

FIG. 4D illustrates a cross-sectional view of another illustrative,non-limiting embodiment of the wound healing apparatus of FIG. 4A;

FIG. 4E illustrates a cross-sectional view of another illustrative,non-limiting embodiment of the wound healing apparatus of FIG. 4A;

FIG. 5A illustrates a cross-sectional view of another illustrative,non-limiting embodiment of a wound healing apparatus in a state forpromoting epithelialisation;

FIG. 5B illustrates a cross-sectional view of the wound healingapparatus of FIG. 5A in a state for promoting granulation;

FIG. 6A illustrates a cross-sectional view of another illustrative,non-limiting embodiment of a wound healing apparatus in a state forpromoting epithelialisation;

FIG. 6B illustrates a cross-sectional view of the wound healingapparatus of FIG. 6A in a state for promoting granulation;

FIG. 7A illustrates a cross-sectional view of another illustrative,non-limiting embodiment of a wound healing apparatus in a state forpromoting epithelialisation;

FIG. 7B illustrates a cross-sectional view of the wound healingapparatus of FIG. 7A in a state for promoting granulation;

FIG. 8A illustrates a cross-sectional view of another illustrative,non-limiting embodiment of a wound healing apparatus in a state forpromoting epithelialisation;

FIG. 8B illustrates a cross-sectional view of the wound healingapparatus of FIG. 8A in a state for promoting granulation;

FIG. 9A illustrates a cross-sectional view of another illustrative,non-limiting embodiment of a wound healing apparatus with a hydrogel inan unexpanded state; and

FIG. 9B illustrates a cross-sectional view of the wound healingapparatus of FIG. 9A with the hydrogel in an expanded state.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following detailed description of several illustrativeembodiments, reference is made to the accompanying drawings that form apart hereof, and in which is shown by way of illustration specificpreferred embodiments in which the invention may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is understood that otherembodiments may be utilized and that logical structural, mechanical,electrical, and chemical changes may be made without departing from thespirit or scope of the invention. To avoid detail not necessary toenable those skilled in the art to practice the embodiments describedherein, the description may omit certain information known to thoseskilled in the art. The following detailed description is, therefore,not to be taken in a limiting sense, and the scope of the illustrativeembodiments are defined only by the appended claims. Unless otherwiseindicated, as used herein, “or” does not require mutual exclusivity.

The term “reduced pressure” as used herein generally refers to apressure less than the ambient pressure at a tissue site that is beingsubjected to treatment. In most cases, this reduced pressure will beless than the atmospheric pressure at which the patient is located.Alternatively, the reduced pressure may be less than a hydrostaticpressure associated with tissue at the tissue site. Although the terms“vacuum” and “negative pressure” may be used to describe the pressureapplied to the tissue site, the actual pressure reduction applied to thetissue site may be significantly less than the pressure reductionnormally associated with a complete vacuum. Reduced pressure mayinitially generate fluid flow in the area of the tissue site. As thehydrostatic pressure around the tissue site approaches the desiredreduced pressure, the flow may subside, and the reduced pressure is thenmaintained. Unless otherwise indicated, values of pressure stated hereinare gauge pressures. Similarly, references to increases in reducedpressure typically refer to a decrease in absolute pressure, whiledecreases in reduced pressure typically refer to an increase in absolutepressure.

Referring to FIG. 1, an illustrative embodiment of a reduced pressuretreatment system 100 for treating a tissue site 101 on a patient withreduced pressure includes a dressing 102 placed proximate to the tissuesite 101 and a reduced pressure treatment device 104 fluidly coupled tothe dressing 102. The dressing 102 includes a wound healing apparatus106 for promoting both granulation and epithelialisation of the tissuesite 101. As used herein, the term “tissue site” may refer to a wound,such as a wound 105, or defect located on or within any tissue,including but not limited to, bone tissue, adipose tissue, muscletissue, neural tissue, dermal tissue, vascular tissue, connectivetissue, cartilage, tendons, or ligaments. The term “tissue site” mayfurther refer to areas of any tissue that are not necessarily wounded ordefective, but are instead areas in which it is desired to add orpromote the growth of additional tissue. For example, reduced pressuretissue treatment may be used in certain tissue areas to grow additionaltissue that may be harvested and transplanted to another tissuelocation.

The wound healing apparatus 106 may be a manifold or fluidly connectedto a manifold. The term “manifold” as used herein generally refers to asubstance or structure that is provided to assist in applying reducedpressure to, delivering fluids to, or removing fluids from the tissuesite 101. The manifold typically includes a plurality of flow channelsor pathways that distribute fluids provided to and removed from thetissue site around the manifold. In one illustrative embodiment, theflow channels or pathways are interconnected to improve distribution offluids provided or removed from the tissue site 101. Examples ofmanifolds may include, for example, without limitation, devices thathave structural elements arranged to form flow channels, such as, forexample, cellular foam, open-cell foam, porous tissue collections,liquids, gels, and foams that include, or cure to include, flowchannels. In one embodiment, the wound healing apparatus 106 includes aporous foam and having a plurality of interconnected cells or pores thatact as flow channels. The porous foam may be a polyurethane, open-cell,reticulated foam such as GranuFoam® material manufactured by KineticConcepts, Incorporated of San Antonio, Tex. Other embodiments mayinclude “closed cells.”

The dressing 102 further includes a reduced pressure interface 108fluidly coupled to the wound healing apparatus 106 and a drape 110. Inone embodiment, a manifold (not shown) is positioned between the reducedpressure interface 108 and the wound healing apparatus 106 fordistributing pressure or facilitating fluid communication between thereduced pressure interface 108 and the wound healing apparatus 106. Thedrape 110, or cover, may be placed over the wound healing apparatus 106and a portion of a patient's epidermis 103 to create a fluid sealbetween the drape 110 and the epidermis 103. The drape 110 may includean adhesive 109 or bonding agent to secure the drape 110 to theepidermis 103. In one embodiment, the adhesive 109 may be used to createa seal between the drape 110 and the epidermis 103 to prevent leakage ofreduced pressure from the tissue site 101. In another embodiment, a seallayer (not shown) such as, for example, a hydrogel or other material maybe disposed between the drape 110 and the epidermis 103 to augment orsubstitute for the sealing properties of the adhesive 109. As usedherein, “fluid seal” means a seal adequate to maintain reduced pressureat a desired site given the particular reduced pressure source involved.

The reduced pressure interface 108 may be positioned adjacent to orcoupled to the drape 110 to provide fluid access to the wound healingapparatus 106. The drape 110 has an aperture 113 for providing fluidaccess to the reduced pressure interface 108. In one embodiment, thedrape 110 is placed over the reduced pressure interface 108 and aportion of the patient's epidermis 103 to create a fluid seal betweenthe drape 110 and the epidermis 103. A reduced pressure delivery conduit112 fluidly couples the reduced pressure treatment device 104 and thereduced pressure interface 108. The reduced pressure interface 108allows the reduced pressure to be delivered to the tissue site 101.While the amount and nature of reduced pressure applied to the tissuesite 101 will typically vary according to the application, in oneembodiment, the reduced pressure treatment device 104 may providereduced pressures between about 0 mm Hg and about −500 mm Hg and morespecifically between about −125 mm Hg and about −300 mm Hg for promotinggranulation, and between about 0 mm Hg and about −125 mm Hg forpromoting epithelialisation.

The reduced pressure treatment device 104 may include a collectioncanister 114 in fluid communication with a reduced pressure source 116.The reduced pressure delivery conduit 112 may be a multi-lumen tube thatprovides a continuous conduit between the reduced pressure interface 108and an inlet 119 positioned on the collection canister 114. Liquids orexudates communicated from the wound healing apparatus 106 through thereduced pressure delivery conduit 112 are removed from the reducedpressure delivery conduit 112 and retained within the collectioncanister 114.

In the embodiment illustrated in FIG. 1, the reduced pressure source 116is an electrically-driven vacuum pump. In another implementation, thereduced pressure source 116 may instead be a manually-actuated ormanually-charged pump that does not require electrical power. Thereduced pressure source 116 instead may be any other type of reducedpressure pump, or alternatively a wall suction port such as thoseavailable in hospitals and other medical facilities. The reducedpressure source 116 may be housed within or used in conjunction with thereduced pressure treatment device 104, which may also contain sensors,processing units, alarm indicators, memory, databases, software, displayunits, and user interfaces 111 that further facilitate the applicationof reduced pressure treatment to the tissue site 101. In one example,pressure-detection sensors (not shown) may be disposed at or near thereduced pressure source 116. The pressure-detection sensors may receivepressure data from the reduced pressure interface 108 via lumens in thereduced pressure delivery conduit 112 that are dedicated to deliveringreduced pressure data to the pressure-detection sensors. Thepressure-detection sensors may communicate with a processing unit thatmonitors and controls the reduced pressure that is delivered by thereduced pressure source 116.

Referring now to FIGS. 2A and 2B, an illustrative embodiment of thewound healing apparatus 106 positioned proximate the tissue site 101 andcovered with the drape 110 is presented in more detail. The woundhealing apparatus 106 includes a plurality of projections 120 extendingfrom a mat 118. In one embodiment, the mat 118 may be substantially gasimpermeable and flexible. The wound healing apparatus 106 has a firstconfiguration for promoting epithelialisation as shown in FIG. 2A and asecond configuration for promoting granulation as shown in FIG. 2B. Inthe first configuration shown in FIG. 2A, a flexible membrane 130 coversthe projections 120 and presents a substantially smooth surface to thetissue site 101. When the tissue site 101 is exposed to a substantiallysmooth surface in the presence of reduced pressure, epithelialisation isencouraged. When reduced pressure and a more rough surface such as thatshown in FIG. 2B is presented to the tissue site 101, granulation isencouraged. As illustrated in FIG. 2B, the projections 120 are capableof deforming the flexible membrane 130 to present a rougher surface tothe tissue site 101. The rough surface presented by the projections 120causes microstrains and microstresses to be applied to the tissue site101, which increases granulation.

The substantially gas impermeable, flexible mat 118 includes a pluralityof channels 128 for allowing the passage of fluids through the mat 118to or from the tissue site 101. The substantially gas impermeable,flexible mat 118 may, for example, be a polyurethane (PU), thermoplasticelastomer (TPE), or silicone elastomer material. The plurality ofprojections 120 extend from a surface 122 of the substantially gasimpermeable, flexible mat 118 and may be in fluid communication with thesubstantially gas impermeable, flexible mat 118. Each projection 120 hasa first end 124 connected to the surface 122 of the substantially gasimpermeable, flexible mat 118 and a second end 126 opposing the firstend 124. The first end 124 of each projection 120 may be bonded orsimilarly fixed to the surface 122. The plurality of projections 120 maybe any shape or size; for example the plurality of projections 120 maybe spikes, rods, pins, tubes, or other protrusions, etc. The pluralityof projections 120 may be made from a range of polymers such as apolyurethane (PU), thermoplastic elastomer (TPE), or silicone elastomermaterial and may have a range of compressibility or hardness such as10⁰-100⁰ Shore A. Structurally, the plurality of projections 120 may besolid, perforated, hollow, etc., or any combination thereof. Theconfiguration of the plurality of projections 120 (the shape andstructure) may enable the transmission of pressure and fluid through theplurality of projections 120 as well as modify the compressibility ofthe plurality of projections 120 depending on the material used.

The second end 126 of at least a portion of the plurality of projections120 may be covered by the flexible membrane 130. In one embodiment, theflexible membrane 130 may be bonded to at least a portion of theplurality of projections 120 or similarly fixed. The flexible membrane130 is sufficiently flexible to be deformed by at least a portion of theplurality of projections 120 and may be an elastomeric material.“Elastomeric” means having the properties of an elastomer, and generallyrefers to a polymeric material that has rubber-like properties. Morespecifically, most elastomers have elongation rates greater than 100%and a significant amount of resilience. The resilience of a materialrefers to the material's ability to recover from an elastic deformation.Examples of elastomers may include, but are not limited to, naturalrubbers, polyisoprene, styrene butadiene rubber, chloroprene rubber,polybutadiene, nitrile rubber, butyl rubber, ethylene propylene rubber,ethylene propylene diene monomer, chlorosulfonated polyethylene,polysulfide rubber, polyurethane, EVA film, co-polyester, thermoplasticelastomers, synthetic latexes, and silicones. The flexible membrane 130may be hydrophilic or hydrophobic.

The flexible membrane 130 may be deformed by the plurality ofprojections 120 when a biasing force, or other activation stimulus, isexerted on the substantially gas impermeable, flexible mat 118 and thebiasing force is greater than or equal to a threshold force. In oneembodiment, the flexible membrane 130 may be deformed by the pluralityof projections 120 when the biasing force exerted on the plurality ofprojections 120 is greater than or equal to the threshold force. Thedeformation of the flexible membrane 130 may be in response to acombination of the biasing force exerted on the mat 118 or projections120 and the force exerted by the tissue site on portions of the flexiblemembrane 130 between the projections 120. While the deformation of theflexible membrane 130 may occur as described above when the biasingforce equals or exceeds a threshold force, the deformation may occurmore gradually over a range of forces.

The biasing force may be in the form of reduced pressure supplied fromthe reduced pressure source 116. As the reduced pressure beneath thedrape 110 increases (i.e. the gauge pressure decreases), the drape 110is pulled toward the tissue site, which exerts a biasing force on theflexible mat 118 by the drape 110. In a specific, non-limitingembodiment, the amount of reduced pressure required for the biasingforce to equal the threshold force may be about −125 mm Hg. In otherembodiments, the biasing force may be applied to the flexible mat 118 bya weight or any other force that is not generated by a reduction inpressure beneath the drape 110 but that promotes either rough or smoothsurfaces to encourage granulation or epithelialisation.

Microperforations (not shown) or valves that expand or open under theinfluence of the biasing force may be present on the flexible membrane130. In one embodiment, the microperforations are small apertures thatextend through the flexible membrane 130. The size of themicroperforations is such that when the flexible membrane 130 is notexpanded, the microperforations are essentially closed thereby notallowing the transmission of pressure and fluids through the flexiblemembrane 130. As the flexible membrane 130 expands under the influenceof the biasing force, the deformation of the flexible membrane 130 bythe plurality of projections 120 expands the microperforations, whichallows for the transmission of pressure and fluids. Small valves may beeither operably associated with the microperforations or otherwiseassociated with the flexible membrane 130 to further control the passageof pressure and fluids through the flexible membrane 130. In oneembodiment, the microperforations may be positioned directly beneatheach of the projections 120. In another embodiment, themicroperforations may be positioned in the flexible membrane 130 betweenprojections 120. A sufficiently smooth surface for encouragingephithelialization is presented when the microperforations are closed orthe flexible membrane 130 is in an unexpanded state. In one embodiment,using the Verein Deutscher Ingenieure (VDI) (3400) standard scale, asufficiently smooth surface for promoting epithelialisation may have asurface finish of VDI (3400)<30. In a specific, non-limiting embodiment,the microperforations may be closed when the biasing force is at reducedpressure levels less than about −50 mm Hg (i.e. at gauge pressuresgreater than about −50 mmHg). Pressures in a range between about −50 mmHg and about −125 mm Hg may be sufficient to cause the microperforationsto open and expand without causing the flexible membrane 130 to deform.When the flexible membrane 130 is deformed by the plurality ofprojections 120, the microperforations may also expand to allow for thetransmission of pressure and fluids. The deformation of the flexiblemembrane 130 presents a rough, porous surface to the tissue site 101 forencouraging granulation. In one embodiment, a rough, porous surface mayhave a surface finish of VDI (3400)>30.

In operation, a health care provider may place the wound healingapparatus 106 proximate the tissue site 101 and cover the wound healingapparatus 106 with the drape 110 to create a fluid seal beneath thedrape. In one embodiment, a manifold may be placed between the drape 110and the wound healing apparatus 106. The wound healing apparatus 106 isthen fluidly connected to the reduced pressure treatment device 104.Reduced pressure is supplied to the tissue site 101 via the woundhealing apparatus 106. The health care provider may adjust the levels ofreduced pressure supplied depending on the type of treatment sought. Inone embodiment, to promote granulation the health care provider mayincrease the reduced pressure to levels equal to or greater than about−125 mm Hg thereby causing the flexible membrane 130 to deform andpresent a rough, porous surface to the tissue site 101. In the presenceof this reduced pressure, the rough surface presented by the projections120 of the wound healing apparatus 106 exert a force on the tissue site101. This force creates microstrains and microstresses at the tissuesite 101, which promotes development of new granulation tissue. Topromote epithelialisation, the heath care provider may decrease thereduced pressure to levels less than about −125 mm Hg. These reducedpressure levels allow the projections to essentially retract such thatthe projections 120 no longer deform the flexible membrane 130. Theflexible membrane 130 is therefore capable of presenting a smoothsurface to the tissue site 101 which is more conducive to promotingepithelialisation. In one embodiment, at reduced pressure levels betweenabout −50 mm Hg and about −125 mm Hg, the flexible membrane 130 isrelatively smooth, and yet the microperforations or valves associatedwith the flexible membrane 130 are open, thereby allowing improved fluidremoval. At reduced pressure levels less than about −50 mm Hg, theflexible membrane 130 remains smooth, and the microperforations orvalves are substantially closed. Again, the smooth surface encouragesepithelialisation, and the reduced pressure aids in fluid removal,although not as much fluid as if the mircoperforations or valves wereopen. While specific pressure values have been presented as an example,it should be recognized that the wound healing apparatus 106 could beconfigured to allow deformation of the flexible membrane 130 at higheror lower pressures, thereby altering the reduced pressures required topromote either granulation or epithelialisation.

Referring now primarily to FIG. 3, but also to FIGS. 1, 2A, and 2B,another illustrative embodiment of the wound healing apparatus 106 ofFIGS. 1, 2A, and 2B is presented. In this embodiment, the wound healingapparatus 106 includes the substantially gas impermeable, flexible mat118 and the plurality of projections 120 but not the flexible membrane130. The plurality of projections 120 may be constructed frombioabsorbable materials that do not have to be removed from a patient'sbody following use of the wound healing apparatus 106. Suitablebioabsorbable materials may include, without limitation, a polymericblend of polylactic acid (PLA) and polyglycolic acid (PGA). Thepolymeric blend may also include without limitation polycarbonates,polyfumarates, and capralactones. Additionally, each of the plurality ofprojections 120 may vary in shape, size, and structure relative to eachother.

The presence of fluid may cause the plurality of projections 120 todissolve. The fluid may be exudate or other fluids from the tissue site101, or the fluid may be instilled into the tissue site 101 by a healthcare provider or a device associated with the reduced pressure treatmentdevice 104 to accelerate dissolution of the plurality of projections120. The fluid may be instilled into the tissue site 101 via thesubstantially gas impermeable, flexible mat 118 or the plurality ofprojections 120. In one embodiment, hollow or perforated projections(not shown) may communicate fluid into the tissue site 101. Theplurality of projections 120 may include treatment agents such as growthfactors, anti-bacterials, debriding agents, pro or anti-clogging agents,pain reducing agents, etc. that are released into the tissue site 101 asthe plurality of projections 120 dissolve.

In operation, the wound healing apparatus 106 having the plurality ofbioabsorbable projections 120 may be placed proximate the tissue site101, covered with the drape 110, and fluidly connected to the reducedpressure source 116 (FIG. 1) so as to receive reduced pressure. Theplacement of the plurality of projections 120 into the tissue site 101presents a sufficiently rough surface to promote granulation. When theplurality of projections 120 dissolve in the presence of fluid, thesubstantially gas impermeable, flexible mat 118 presents a sufficientlysmooth surface to the tissue site 101 to promote epithelialisation. Aspreviously stated, differing levels of reduced pressure may be useddepending on the type of treatment desired.

Referring now to FIGS. 4A and 4B, another illustrative embodiment of awound healing apparatus 206 for use in a reduced pressure treatmentsystem (e.g., the reduced pressure treatment system 100 of FIG. 1) ispresented. As shown, the wound healing apparatus 206 is positionedproximate the tissue site 101 and covered with the drape 110. The woundhealing apparatus 206 includes a hollow mat 208 having an inner chamber211 and a plurality of recesses 212 disposed in proximity to a firstsurface 214 of the hollow mat 208. An extendable projection 216 ispositioned within each of the plurality of recesses 212 and isconfigured to extend from the recesses 212 when a pressure (p₁) withinthe inner chamber 211 is greater than a pressure (p₂) outside of theinner chamber 211 (e.g. in the recesses 212). The wound healingapparatus 206 has a first configuration for promoting epithelialisationas shown in FIG. 4A in which a relatively smooth surface is presented tothe tissue site 101. In a second configuration shown in FIG. 4B, thewound healing apparatus 206 has a second configuration for promotinggranulation in which a relatively rough surface is presented to thetissue site 101. As previously described, the relatively rough surfacepresented by the extension of projections 216 induces microstrains andmicrostresses at the tissue site 101 which are conducive to newgranulation tissue growth.

The hollow mat 208 may be formed from a polymeric material and may bepre-sealed so that the fluid volume within the inner chamber 211 remainsstatic during treatment. The hollow mat 208 may be formed with aplurality of sealed channels (not shown) disposed therethrough thatextend from a second surface 215 to the first surface 214 to facilitatethe transmission of fluid and pressure. The hollow mat 208 includes theplurality of recesses 212 for housing the extendable projections 216.The extendable projections 216 remain sheathed within the recesses 212when the pressure (p₂) in the recesses 212 is greater than the pressure(p₁) within the inner chamber 211. When the extendable projections 216are sheathed as shown in FIG. 4A, the wound healing apparatus 206presents a sufficiently smooth surface to the tissue site 101 to promoteepithelialisation. In one embodiment, a sufficiently smooth surface mayhave a surface finish of VDI (3400)<30. In the event the pressure (p₁)within the inner chamber 211 becomes greater than the pressure (p₂) inthe recesses 212, the recesses 212 have one or more side walls 240configured to collapse or compress, thereby allowing the extendableprojections 216 to extend from the plurality of recesses 212 and contactthe tissue site 101. When the extendable projections 216 extend into thetissue site 101, a sufficiently rough and uneven surface is presented tothe tissue site for promoting granulation. In one embodiment, asufficiently rough and uneven surface may have a surface finish of VDI(3400)>30. It should be understood that the extendable projections 216may be any shape or size; for example the extendable projections 216 maybe spikes, rods, pins, tubes, or other protrusions, etc. Additionally,the extendable projections 216 may be made from a range of low densitypolymers such as a thermoplastic elastomer (TPE) and may have a range ofcompressibility or hardness such as 10 ⁰-100⁰ Shore A. Low densitypolymers may be used so that the weight of the extendable projections216 does not force the extendable projections 216 from the recesses 212(i.e., due to gravity).

The wound healing apparatus 206 may further include a pressurizationunit 218 for changing the pressure (p₁) within the inner chamber 211. Inone embodiment, the pressure (p₁) within the inner chamber 211 may bechanged using the pressurization unit 218 through pneumatic or hydraulicmeans. The pressurization unit 218 is fluidly connected to the hollowmat 208 and may be placed adjacent the second surface 215. Thepressurization unit 218 may be sealed beneath the drape 110 with aconnecting tube 220 extending through an aperture 222 in the drape 110.In one embodiment (not shown), the pressurization unit 218 may be placedoutside the drape 110 and fluidly connected to the hollow mat 208through an aperture in the drape 110. In another embodiment, atmosphericair could be supplied to the inner chamber 211 when the reduced pressureis applied to the wound healing apparatus 206 thereby allowing thepressure (p₁) within the inner chamber 211 to be greater than thepressure (p₂) in the recesses 212. Alternatively, if the inner chamber211 is sealed as previously described, and the pressure of air withinthe inner chamber 211 is at approximately atmospheric pressure, theapplication of reduced pressure beneath the drape 110 will result in anextension of the projections 216.

In operation, a health care provider may place the wound healingapparatus 206 proximate the tissue site 101 and cover the wound healingapparatus 206 with the drape 110 to create a sealed space 224 beneaththe drape. In one embodiment, a manifold may be placed between the drape110 and the wound healing apparatus 206. The sealed space 224 is thenfluidly connected to a reduced pressure treatment device. Reducedpressure is supplied to the tissue site 101 at desired treatment levels.In one embodiment, the wound healing apparatus 206, or the hollow mat208, is pre-sealed so that the level of reduced pressure supplied to thesealed space 224 determines whether the wound healing apparatus 206 isconfigured to promote granulation or epithelialisation, i.e., whetherthe pressure (p₂) in the recesses 212 is less than or greater than thepressure (p₁) within the inner chamber 211 of the hollow mat 208. Inanother embodiment, the pressure (p₁) within the inner chamber 211 maybe changed by the pressurization unit 218. In this instance, both thepressurization unit 218 and the level of reduced pressure supplied tothe sealed space determines whether the wound healing apparatus 206 isconfigured to promote either granulation or epithelialisation, orcombinations thereof. In some embodiments, it may be desired toconfigure the wound healing apparatus 206 such that granulation ispromoted in one area of the tissue site while epithelialisationsimultaneously is promoted at another area of the tissue site. This maybe accomplished by only presenting projections or a rough surface to thetissue site in areas where granulation is desired. In those areas whereepithelialisation is desired, a smoother surface would be presented tothe tissue site.

Referring now primarily to FIGS. 4C-4E, but still with reference toFIGS. 4A and 4B, the wound healing apparatus 206 is further shown inalternative embodiments that include a flexible membrane 230 placed overthe plurality of recesses 212 covering the extendable projections 216.The flexible membrane 230 may be bonded or similarly fixed to the hollowmat 208 and may be an elastomeric material that is hydrophilic orhydrophobic. A hydrogel-material may be included with the flexiblemembrane 230 for helping the flexible membrane 230 present a smoothsurface to the tissue site 101 when activated by fluids.Microperforations (not shown) or valves may be present on the flexiblemembrane 230 for aiding in the transmission of pressure and fluids. InFIG. 4C, the flexible membrane 230 is continuous and may be deformed bythe extendable projections 216 when the pressure (p₁) within the innerchamber 211 becomes greater than the pressure (p₂) in the recesses 212.The deformation of the flexible membrane 230 by the extendableprojections 216 presents a sufficiently rough and uneven surface to thetissue site 101 for promoting granulation. In FIG. 4D, the flexiblemembrane 230 has slits coinciding with each extendable projection 216 sothat when the pressure (p₁) within the inner chamber 211 is greater thanthe pressure (p₂) in the recesses 212, the extendable projection 216deforms the slits on the flexible membrane 230 allowing a portion of theextendable projection 216 to be in direct contact with the tissue site101. In FIG. 4E, the flexible membrane 230 has flaps coinciding witheach extendable projection 216. The flaps completely covers theplurality of recesses 212 when the pressure (p₁) within the innerchamber 211 is less than the pressure (p₂) in the recesses 212. When thepressure (p₁) within the inner chamber 211 is greater than the pressure(p₂) in the recesses 212, the extendable projection 216 deforms theflaps on the flexible membrane 230 allowing a portion of the extendableprojection 216 to be in direct contact with the tissue site 101. The useof the flexible membrane 230 may aid the wound healing apparatus 206 inthe epithelialisation configuration by helping to present a sufficientlysmooth surface to the tissue site. The flexible membrane 230 may be usedwith any of the disclosed embodiments for the wound healing apparatus206.

Referring now to FIGS. 4A-5B and specifically to FIGS. 5A and 5B,another illustrative embodiment of the wound healing apparatus 206 ofFIGS. 4A, and 4B is presented. As presented, the wound healing apparatus206 has a first configuration for promoting epithelialisation shown inFIG. 5A and a second configuration for promoting granulation shown inFIG. 5B. In this embodiment, the extendable projections 216 have atelescoping configuration. The extendable projections 216 include afirst section 236, a second section 234, and a third section 232. Whenthe pressure (p₁) within the inner chamber 211 is less than the pressure(p₂) in the recesses 212, the first section 236, the second section 234,and the third section 232 remain tucked within the recesses 212presenting a smooth surface to the tissue site 101 for promotingepithelialisation. When the pressure (p₁) within the inner chamber 211is greater than a pressure (p₂) in the recesses 212, the extendableprojections 216 extend from the recesses 212 in a telescopingconfiguration for promoting granulation. In the telescopingconfiguration, the third section 232 extends beyond the first surface214 of the hollow mat 208, the second section 234 extends beyond thethird section 232, and the first section 236 extends beyond the secondsection 234.

Referring now to FIGS. 4A, 4B, 6A, and 6B and specifically to FIGS. 6Aand 6B, another illustrative embodiment of the wound healing apparatus206 of FIGS. 4A, and 4B is presented. As shown, the wound healingapparatus 206 has a first configuration for promoting epithelialisationas shown in FIG. 6A and a second configuration for promoting granulationas shown in FIG. 6B. In this embodiment, the plurality of recesses 212have a bellows configuration. In the bellows configuration, theplurality of recesses 212 have one or more side walls 240 that may beeither corrugated, comprised of a plurality of interleaved bends, orcomprised of a plurality of furrows. The one or more side walls 240 areconfigured to collapse when the pressure (p₁) within the inner chamber211 is greater than a pressure (p₂) in the recesses 212 so that theextendable projections 216 may extend from the recesses 212 and into thetissue site 101.

Referring now to FIGS. 4A, 4B, 7A, and 7B and specifically to FIGS. 7Aand 7B, another illustrative embodiment of the wound healing apparatus206 of FIGS. 4A, and 4B is presented. As shown, the wound healingapparatus 206 has a first configuration for promoting epithelialisationas shown in FIG. 7A and a second configuration for promoting granulationas shown in FIG. 7B. In this embodiment, the extendable projections 216are connected to the flexible membrane 230 that may be an elastomericmaterial. When the pressure (p₁) within the inner chamber 211 is lessthan the pressure (p₂) in the recesses 212, the extendable projections216 are tucked inside the recesses 212 and flush with the first surface214, presenting a smooth surface to the tissue site 101 for promotingepithelialisation. When the pressure (p₁) within the inner chamber 211is greater than a pressure (p₂) in the recesses 212, the flexiblemembrane extends beyond the first surface 214 pushing the extendableprojections 216 into the tissue site 101 for promoting granulation.

The various configuration of wound healing apparatus 206 illustrated inFIGS. 4A, 4B, 4C, 4D, 4E, 5A, 5B, 6A, 6B, 7A, and 7B may, in operation,be subjected to reduced pressures similar to those described previouslywith reference to wound healing apparatus 106.

Depending on the configuration of the wound healing apparatus 206, aparticular pressure or range of pressures may be used to alter a surfaceof the wound healing apparatus 206 adjacent the tissue site, therebyencouraging granulation or epithelialisation.

Referring now to FIGS. 8A and 8B, an illustrative embodiment of a woundhealing apparatus 306 positioned proximate the tissue site 101 andcovered with the drape 110 is presented. The wound healing apparatus 306may be used with a reduced pressure treatment system such as the reducedpressure treatment system 100 of FIG. 1. The wound healing apparatus 306includes a porous pad 332 and a plurality of granulation promoters 320embedded within the porous pad 332. The wound healing apparatus 306 hasa first configuration for promoting epithelialisation as shown in FIG.8A and a second configuration for promoting granulation as shown in FIG.8B.

The porous pad 332 may be made of a polyurethane, open-cell, reticulatedfoam such as GranuFoam® material manufactured by Kinetic Concepts,Incorporated of San Antonio, Tex. The porous pad 332 has a firstcompressibility (C₁) less than a second compressibility (C₂) of theplurality of granulation promoters 320; i.e., the porous pad 332 issofter than, and will compress before, the plurality of granulationpromoters 320. The porous pad 332 may help distribute any forces (e.g.,body weight) applied to the wound healing apparatus 306 when reducedpressure is not applied to minimize potential high pressure points atthe tissue site 101 caused from the plurality of granulation promoters320.

The plurality of granulation promoters 320 may be any shape or size; forexample the plurality of granulation promoters 320 may be spikes, rods,pins, tubes, or other protrusions, etc. The plurality of granulationpromoters 320 may be made from a range of polymers such as apolyurethane (PU), thermoplastic elastomer (TPE), or silicone elastomermaterial and thus, the second compressibility (C₂) may have a range ofcompressibility or hardness such as 10⁰-100⁰ Shore A. In a complementaryfashion, the first compressibility (C₁) of the porous pad 332 may have acompressibility or hardness of <10⁰-<100⁰ Shore A, depending on thesecond compressibility (C₂) of the plurality of granulation promoters320 and the degree of granulation desired. Structurally, the pluralityof granulation promoters 320 may be solid, perforated, hollow, etc., orany combination thereof. Additionally, the plurality of granulationpromoters 320 may be bioabsorbable and may contain a hydrogel-formingmaterial. In one embodiment, the porous pad 332 may contain ahydrogel-forming material to promote epithelialisation as a liquid isintroduced to the porous pad. The configuration of the plurality ofgranulation promoters 320 (the shape and structure) may enable thetransmission of pressure and fluid through the plurality of granulationpromoters 320 as well as modify the compressibility of the plurality ofgranulation promoters 320 depending on the material used.

The plurality of granulation promoters 320 may be near a tissue-facingside 334 of the porous pad 332, and in one embodiment, the plurality ofgranulation promoters 320 may extend from a surface 322 of asubstantially gas impermeable, flexible mat 318 in a similar manner asdescribed with reference to the wound healing apparatus 106 of FIGS. 2Aand 2B.

The wound healing apparatus 306 may include a flexible membrane 330positioned adjacent the tissue-facing side 334 of the porous pad 332.The flexible membrane 330 is sufficiently flexible to be deformed by atleast a portion of the plurality of granulation promoters 320. Theflexible membrane 330 may be an elastomeric material.

The flexible membrane 330 may be deformed by the plurality ofgranulation promoters 320 when a biasing force, or other activationstimulus, is exerted on the porous pad 332 or the substantially gasimpermeable, flexible mat 318 and the biasing force is greater than orequal to a threshold force. When the biasing force is greater than orequal to a threshold force, the plurality of granulation promoters 320extend from the porous pad 332 or alter the tissue-facing side 334 ofthe porous pad 332. In one embodiment, the flexible membrane 330 may bedeformed by the plurality of granulation promoters 320 when the biasingforce exerted on the plurality of granulation promoters 320 is greaterthan or equal to the threshold force. The biasing force may be in theform of reduced pressure supplied from the reduced pressure source 116of FIG. 1. In a specific, non-limiting embodiment, the threshold forcemay be a pressure greater than or equal to about −125 mm Hg.

The flexible membrane 330 may include microperforations (not shown) orvalves that may expand under the influence of the biasing force. In oneembodiment, the microperforations expand when the flexible membrane 330is deformed by the plurality of granulation promoters 320 to allow forthe transmission of pressure and fluids. The microperforations may bepositioned so as to coincide with each of the granulation promoters 320.A sufficiently smooth surface for encouraging epithelialisation ispresented when the microperforations are closed or the flexible membrane330 is in an unexpanded state. In one embodiment, using the VereinDeutscher Ingenieure (VDI) (3400) standard scale, a sufficiently smoothsurface for promoting epithelialisation may have a surface finish of VDI(3400)<30. In a specific, non-limiting embodiment, the microperforationsmay be closed when the biasing force is at pressures less than about −50mm Hg. Pressures in a range between about −50 mm Hg and—about −125 mm Hgmay be sufficient to cause the microperforations to open and expandwithout causing the flexible membrane 330 to deform and the porous pad332 to compress. When the flexible membrane 330 is deformed by theplurality of projections 120 and the porous pad 332 compresses, themicroperforations may also expand to allow for the transmission ofpressure and fluids. The deformation of the flexible membrane 330 andthe compression of the porous pad 332 presents a rough, porous surfaceto the tissue site 101 for encouraging granulation. In one embodiment, arough, porous surface may have a surface finish of VDI (3400)>30.

The wound healing apparatus 306 illustrated in FIGS. 8A and 8B may, inoperation, be subjected to reduced pressures similar to those describedpreviously with reference to wound healing apparatus 106. Depending onthe configuration of the wound healing apparatus 306, a particularpressure or range of pressures may be used to alter a surface of thewound healing apparatus 306 adjacent the tissue site, therebyencouraging granulation or epithelialisation.

Referring now to FIGS. 9A and 9B, an illustrative embodiment of a woundhealing apparatus 406 positioned proximate the tissue site 101 andcovered with the drape 110 is presented. The wound healing apparatus 406includes a granulation-promoting material having a hydrogel-formingmaterial 408 in a least a portion of the granulation-promoting material.In one embodiment, the granulation-promoting material is a porous,reticulated foam 404. The wound healing apparatus 406 has a firstconfiguration for promoting epithelialisation as shown in FIG. 9B and asecond configuration for promoting granulation as shown in FIG. 9A.

The porous, reticulated foam 404 may be an polyurethane, open-cell,reticulated foam such as GranuFoam® material manufactured by KineticConcepts, Incorporated of San Antonio, Tex. The porous, reticulated foam404 has a tissue-contacting surface 412 that is sufficiently rough topromote granulation. When moisture in an amount greater than themoisture content of the gel is presented to the porous, reticulated foam404, the porous, reticulated foam 404 causes the hydrogel-formingmaterial to moisten and expand, thereby altering the tissue-contactingsurface 412 to be sufficiently smooth to promote epithelialisation. Thealtered tissue-contacting surface 412 presents a moist, smooth surfaceto the tissue site 101. The tissue-contacting surface 412 may include abase surface 416 and one or more side surfaces 414. In one embodiment,the hydrogel-forming material 408 releases moisture in the presence of areduced pressure greater than a threshold amount causing thehydrogel-forming material 408 to shrink and the porous, reticulated foam404 to present a sufficiently rough surface to promote granulation. Inanother embodiment, the hydrogel-forming material 408 absorbs moisturein the presence of reduced pressure less than the threshold amountcausing the hydrogel-forming material to expand and present thetissue-contacting surface 412 that is sufficiently smooth to promoteepithelialisation.

In an embodiment where the threshold amount is a pressure of about −25mm Hg, gauge pressures between about −25 mm Hg and about −125 mm Hg (andextending beyond about −125 mm Hg) may be applied to the space beneathdrape 110 to promote granulation tissue growth. At these reducedpressures, a sufficient amount of moisture from the hydrogel-formingmaterial 408 is removed, causing the hydrogel-forming material 408 tocontract, thereby exposing the rough surface of the reticulated foam 404to the tissue site 101. The rough surface promotes granulation byexposing the tissue site 101 to microstrains and microstresses. As thegauge pressure beneath the drape 110 is changed to be between about 0 mmHg and about −25 mm Hg, moisture is absorbed by the hydrogel-formingmaterial 408, thereby causing the hydrogel-forming material 408 toexpand such that a smooth surface is presented to the tissue site 101.The hydrogel-forming material 408 retains the moisture even in thepresence of the reduced pressure, which allows continued removal ofexcess exudate from the tissue site 101.

While a number of discrete embodiments have been described, aspects ofeach embodiment may not be specific to only that embodiment and it isspecifically contemplated that features of embodiments may be combinedwith features of other embodiments. It also should be apparent from theforegoing that an invention having significant advantages has beenprovided. While the invention is shown in only a few of its forms, it issusceptible to various changes and modifications without departing fromthe spirit thereof.

1-21. (canceled)
 22. An apparatus for promoting wound healing, theapparatus comprising: a porous pad having a first compressibility; and aplurality of granulation promoters embedded within the porous pad havinga second compressibility less than the first compressibility of theporous pad, the plurality of granulation promoters positioned near asurface of the porous pad such that in the presence of a biasing forceapplied to the porous pad or plurality of granulation promoters that isgreater than or equal to a threshold amount, the plurality ofgranulation promoters are configured to extend from the porous pad oralter the surface of the porous pad to promote granulation.
 23. Theapparatus of claim 22, further comprising a flexible membrane adjacentthe surface of the porous pad, the flexible membrane having a pluralityof microperforations.
 24. The apparatus of claim 22, wherein theplurality of granulation promoters are configured not to extend from theporous pad or alter the surface of the porous pad when the biasing forceis less than the threshold amount.
 25. The apparatus of claim 22,wherein at least a portion of the porous pad includes a hydrogel-formingmaterial to promote epithelialisation.
 26. The apparatus of claim 22,wherein the plurality of granulation promoters are hollow.
 27. Theapparatus of claim 22, wherein the plurality of granulation promotersare bioabsorbable.
 28. The apparatus of claim 22, wherein the pluralityof granulation promoters are comprised of a hydrogel-forming material.29. An apparatus for promoting granulation and epithelialisation of atissue site, the apparatus comprising: a porou foam having atissue-contacting surface that is sufficiently rough to promotegranulation; and a hydrogel-forming material disposed in at least aportion of the porous foam, the hydrogel-forming material configured toalter the tissue-contacting surface to be sufficiently smooth to promoteepithelialisation if liquid is introduced into the porous foam.
 30. Theapparatus of claim 29, wherein the altered tissue-contacting surfacepresents a moist, smooth surface to the tissue site.
 31. The apparatusof claim 29, wherein the tissue-contacting surface has a base surfaceand one or more side surfaces, and wherein the hydrogel-forming materialis configured to expand to alter the base surface and the one or moreside surfaces to be sufficiently smooth to promote epithelialisation.32. The apparatus of claim 29, wherein the hydrogel-forming material isconfigured to release moisture in the presence of a reduced pressuregreater than a threshold amount.
 33. The apparatus of claim 29, whereinthe hydrogel-forming material is configured to absorb liquid and causethe hydrogel-forming material to expand when a reduced pressure is lessthan a threshold amount.
 34. A reduced pressure treatment system foradministering reduced pressure treatment to a tissue site, the reducedpressure treatment system comprising: a reduced pressure source; and amanifold in fluid communication with the reduced pressure source toprovide a reduced pressure to the tissue site, the manifold comprising atissue-contacting surface having a granulation configuration and anepithelialisation configuration, at least one of the granulationconfiguration and the epithelialisation configuration being activated byan activation stimulus.
 35. The reduced pressure treatment system ofclaim 34, wherein the activation stimulus is a biasing force.
 36. Thereduced pressure treatment system of claim 35, wherein the manifoldfurther comprises: a porous pad having a first compressibility; and aplurality of granulation promoters embedded within the porous pad havinga second compressibility less than the first compressibility of theporous pad, the plurality of granulation promoters positioned near asurface of the porous pad such that in the presence of a biasing forceapplied to the porous pad or plurality of granulation promoters that isgreater than or equal to a threshold amount, the plurality ofgranulation promoters are configured to extend from the porous pad oralter the surface of the porous pad to promote granulation.
 37. Thereduced pressure treatment system of claim 34, wherein the activationstimulus is a liquid introduced into the manifold.
 38. The reducedpressure treatment system of claim 37, wherein the manifold furthercomprises: a reticulated foam with the tissue-contacting surface beingsufficiently rough to promote granulation; and a hydrogel-formingmaterial disposed in at least a portion of the reticulated foam, thehydrogel-forming material configured to moisten and expand if liquid isintroduced into the reticulated foam, thereby altering thetissue-contacting surface to be sufficiently smooth to promoteepithelialisation.
 39. The reduced pressure treatment system of claim34, wherein the manifold further comprises: a substantially gasimpermeable, flexible mat; a plurality of projections extending from asurface of the substantially gas impermeable, flexible mat, eachprojection having a first end connected to the surface and a second endopposing the first end; and a flexible membrane positioned adjacent thesecond end of at least a portion of the plurality of projections, theflexible membrane being sufficiently flexible to allow deformation ofthe flexible membrane by the at least the portion of the plurality ofprojections when the activation stimulus is exerted on the substantiallygas impermeable, flexible mat; wherein the flexible membrane is thetissue-contacting surface.
 40. The reduced pressure treatment system ofclaim 34, wherein the manifold further comprises: a hollow mat having aninner chamber and a plurality of recesses disposed in proximity to afirst surface of the hollow mat; and an extendable projection positionedwithin each recess and configured to extend from the recess whenactivated by the activation stimulus; wherein the activation stimulusoccurs when a first pressure within the inner chamber is greater than asecond pressure in the recess.
 41. A reduced pressure treatment systemfor administering reduced pressure treatment to a tissue site, thereduced pressure treatment system comprising: a reduced pressure source;an apparatus fluidly coupled to the reduced pressure source, theapparatus comprising: a mat that is substantially gas-impermeable andflexible, a flexible membrane, and a plurality of projections extendingfrom the mat, the flexible membrane being sufficiently flexible to allowdeformation of the flexible membrane by at least a portion of theplurality of projections when a biasing force exerted on the mat or theplurality of projections is greater than or equal to a threshold force;and a drape formed of substantially impermeable material configured tocover the apparatus and to substantially maintain reduced pressure atthe tissue site.
 42. The reduced pressure treatment system of claim 41further comprising: a manifold fluidly coupled to the reduced pressuresource for receiving the reduced pressure and positioned between theapparatus and the drape to distribute the reduced pressure to theapparatus.
 43. The reduced pressure treatment system of claim 41,wherein reduced pressure from the reduced pressure source creates thebiasing force.
 44. A reduced pressure treatment system for administeringreduced pressure treatment to a tissue site, the reduced pressuretreatment system comprising: a reduced pressure source; an apparatusfluidly coupled to the reduced pressure source, the apparatuscomprising: a hollow mat having an inner chamber and a plurality ofrecesses disposed in proximity to a first surface of the hollow mat, andan extendable projection positioned within each recess and configured toextend from the recess when a first pressure within the inner chamber isgreater than a second pressure in the recess; and a drape formed ofsubstantially impermeable material configured to cover the apparatus andthe tissue site to substantially maintain reduced pressure at the tissuesite.
 45. A reduced pressure treatment system for administering reducedpressure treatment to a tissue site, the reduced pressure treatmentsystem comprising: a reduced pressure source; an apparatus fluidlycoupled to the reduced pressure source, the apparatus comprising: aporous pad having a first compressibility, and a plurality ofgranulation promoters embedded within the porous pad having a secondcompressibility less than the first compressibility of the porous pad,the plurality of granulation promoters positioned near a surface of theporous pad such that in the presence of a biasing force applied to theporous pad or plurality of granulation promoters that is greater than orequal to a threshold amount, the plurality of granulation promotersextend from the porous pad or alter the surface of the porous pad topromote granulation; and a drape formed of substantially impermeablematerial to cover the apparatus and the tissue site to substantiallymaintain reduced pressure at the tissue site.
 46. A reduced pressuretreatment system for administering reduced pressure treatment to atissue site, the reduced pressure treatment system comprising: a reducedpressure source; an apparatus fluidly coupled to the reduced pressuresource, the apparatus comprising: a porous, reticulated foam having atissue-contacting surface that is sufficiently rough to promotegranulation, and a hydrogel-forming material disposed in at least aportion of the porous, reticulated foam such that introduction of aliquid into the porous, reticulated foam causes the hydrogel-formingmaterial to moisten and expand, thereby altering the tissue-contactingsurface to be sufficiently smooth to promote epithelialisation; and adrape formed of substantially impermeable material to cover theapparatus and the tissue site to substantially maintain reduced pressureat the tissue site.
 47. A method for selectively promoting granulationand epithelialisation of a tissue site, the method comprising:positioning a pad having a tissue-contacting surface at the tissue site;applying a first reduced pressure to the tissue site when thetissue-contacting surface is in a first configuration to promotegranulation; changing the first configuration of the tissue-contactingsurface to a second configuration; and applying a second reducedpressure to the tissue site when the tissue-contacting surface is in thesecond configuration to promote epithelialisation.
 48. The method ofclaim 47, wherein the first configuration includes a substantially roughtissue-contacting surface to promote granulation.
 49. The method ofclaim 47, wherein the second configuration includes a substantiallysmooth tissue-contacting surface to promote epithelialisation.
 50. Themethod of claim 47, wherein changing the first configuration to thesecond configuration comprises removing a biasing force applied to thepad.
 51. The method of claim 47, wherein changing the firstconfiguration to the second configuration comprises introducing a liquidto the pad.
 52. The method of claim 51, wherein introducing the liquidfurther comprises absorbing exudate into the pad from the tissue site.53. The method of claim 51, wherein introducing the liquid furthercomprises introducing saline into the pad.
 54. A treatment device forpositioning in contact with a tissue site to be treated, the devicehaving a tissue-facing surface with a roughness which is variabledependent on a physical input.
 55. A treatment device according to claim54, wherein the device comprises a flexible mat with a plurality ofprojections extending from a surface of the mat towards thetissue-facing surface, and a flexible membrane for contact with thetissue site and covering the ends of the projections distal from themat.
 56. A treatment device according to claim 55, wherein the flexiblemembrane distorts towards the flexible mat between the projections toincrease the roughness of the tissue-facing surface.
 57. A treatmentdevice according to claim 55, wherein the mat is substantially fluidimpermeable.
 58. A treatment device according to claim 55, wherein themembrane comprises a plurality of microperforations configured to expandas the membrane distorts.
 59. A treatment device according to claim 58,wherein the microperforations coincide with the projections, such thatthe projections extend through the microperforations to increase thesurface roughness.
 60. A treatment device according to claim 55, furthercomprising: a drape for sealing around the tissue site to create anenclosed space, and a reduced-pressure source for creating a reducedpressure in the enclosed space, wherein the reduced-pressure is thephysical input.
 61. A treatment device according to claim 54 comprisinga hollow mat having a sealed inner chamber with a chamber wall, thechamber wall having a plurality of retractable projections on thetissue-facing surface of the device.
 62. A treatment device according toclaim 54 comprising a hollow mat having an inner chamber with a ventpipe configured for providing a fluid connection to a remote location,the chamber wall having a plurality of retractable projections on thetissue-facing surface of the device.
 63. A treatment device according toclaim 61, wherein the projections are movable between a retractedposition and an extended position dependent on a pressure differentialbetween the inner chamber and outside the inner chamber.
 64. A treatmentdevice according to claim 61, wherein the projections retract intorecesses in the chamber wall.
 65. A treatment device according to claims61, wherein the projections are telescopic to permit movement betweenthe retracted and extended positions.
 66. A treatment device accordingto claims 61, wherein the projections comprise bellows to permitmovement between the retracted and extended positions.
 67. A treatmentdevice according to claim 61, comprising a pump for varying pressurewithin the inner chamber.
 68. A treatment device according to claim 61,further comprising a flexible membrane covering the tissue-facingsurface of the device.
 69. A treatment device according to claim 68,wherein the membrane comprises openings aligned with the projections.